The separation of monocarboxylic acids (formic, acetic, and propionic) from aqueous solutions is still a current issue for both scientific and industrial fields. Reactive extraction with an adequate extractant and diluent system has been focused and researched as an alternative to other separation techniques. Lately, the use of green solvents instead of conventional organic solvents in carboxylic acid extraction has received a great amount of attention. In this aspect, in the present research, the recovery of formic acid (FA), acetic acid (AA), and propionic acid (PA) from aqueous solutions was carried out by reactive extraction with green solvents. In the current reactive study, tributyl phosphate (TBP) has been used as an extractant, and green solvents, cyclopentyl methyl ether (CPME) and 2-methyl­tetra­hydro­furan (2-MeTHF), have been utilized as diluents. The effect of TBP concentration (0.7–5.2 mol·kg–1) on the extraction power was investigated. In addition, the effects of the use of two different green solvents on extraction were also investigated. Distribution coefficient (D), extraction efficiency (E%), and loading factor (Z) values were ascertained and interpreted. D, E, and Z were determined to be in the ranges of 0.289–4.003, 22.41–78.41%, and 0.198–2.218, respectively. It was also observed that, for the studied range, the extractant concentration was increased to be effective when using CPME as the diluent, but a similar effect was not seen when 2-MeTHF was used. However, 2-MeTHF was observed to be a more effective solvent for physical extraction. The extraction efficiency in both diluents increased in the order of PA > AA ≥ FA.

In current investigation, cyclopentyl methyl ether (CMPE) was tested as a novel membrane solvent for acetic acid removal from an aqueous medium in the facilitated bulk liquid membrane (BLM). Tributyl phosphate (TBP) has been utilized as a carrier in CMPE to facilitate acetic acid transport. The influences of various operating factors like carrier concentration in the membrane solvent, receiving phase type, and receiving phase concentration on removal, were analyzed. The uptake was evaluated by means of feed (extraction) and receiving yields. Following this, a mass transfer modelling was established and the mass transfer coefficients were determined. The maximum yields were recorded as 95.4% for extraction and 78.01% for receiving yields at 2 mol · L−1 carrier concentration in membrane solvent, and 4 mol · L−1 NaOH of receiving phase concentration.

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